In various image display devices such as a liquid crystal display device (LCD), a plasma display panel (PDP), an electroluminescent display (ELD) and a cathode ray tube display device (CRT), an optical laminate is disposed on the surface of the display for the purpose of imparting various functions. For that reason, the optical laminate is required to have high physical strengths (for example, scar resistance, etc.), transparency, chemical resistance, weather resistance (for example, resistance to moist heat, resistance to light, etc.) and the like. Also, in order to prevent the attachment of dusts (for example, motes, etc.) which are liable to lower the visibility onto the surface of the optical laminate from occurring, antistatic properties are also required.
In order to impart the antistatic properties, there is known an antireflection film containing a conductive metal oxide (see, for example, JP-A-2005-196122). In the case of using a metal oxide as the conductive material, it is necessary to increase a density of the metal oxide in a conductive layer (antistatic layer) for the purpose of bringing about conductivity. In that case, there is a concern that the transparency, hardness or durability is affected by an influence of excessive addition of the metal oxide.
On the other hand, there is known a laminate using a conductive polymer as the conductive material (see, for example, JP-A-2005-96397). However, in this laminate, a conductive layer was formed of the conductive polymer singly, and this was very inefficient from the standpoints of costs and manufacturing steps. For that reason, it was desired to add a conductive function to a layer having other function.
In the case where a conductive polymer is added in a layer to be provided on the outermost surface of an optical laminate (for example, a low-refractive index layer, a hard coat layer, etc.), or a conductive functional group is introduced into a binder constituting the layer, when the amount of the conductive material is increased until sufficient conductivity is obtained, curing of the binder is impaired, and the necessary physical strengths of the layer (for example, scar resistance, etc.) are lowered. Therefore, it was difficult to provide the layer to be provided on the outermost surface of the optical laminate with an antistatic function. Also, when the conductive polymer is used for a hard coat layer having a thickness of several μm, the use amount of a curable binder increases, and the necessary physical strength is easily obtainable. However, in order to ensure the contact between conductive materials necessary for revealing the conductivity, the use amount of the conductive material increases, and there were involved such problems as coloration and an increase of costs.
In the case of coating a volatile solvent-containing composition containing only a conductive polymer composition and an ionizing radiation curable compound as a binder to prepare a thin film of not more than 1 μm, the liquid viscosity is low so that surface properties of the coating film become non-uniform. In the case where a polymer is added as a thickener to such a composition until the resulting composition has a proper viscosity, the polymer and the conductive polymer composition cause phase separation, resulting in causing such problems as deterioration of surface properties and a lowering of the physical strength or conductivity.
JP-A-2007-185824, JP-A-2005-316425 and JP-A-2007-293325 disclose an embodiment in which an ion-conducting or electron-conducting conductive material is added in a low-refractive index layer.
However, the materials specifically disclosed in the working examples of JP-A-2007-185824, JP-A-2005-316425 and JP-A-2007-293325 are an ion-conducting material, and there was the case where the conductivity is not always sufficient depending upon the environmental moisture. Also, JP-A-2007-185824, JP-A-2005-316425 and JP-A-2007-293325 disclose organic conductive polymer compounds such as polyaniline and polythiophene, both of which are a conductive polymer, as illustrative compounds. However, in the case where such a compound is merely introduced into a coating film as it is, it does not substantially have conductivity and is required to be partially oxidized by doping.
However, when anion doping which is generally used is applied, since the resulting conductive polymer is high in hydrophilicity, it is low in affinity with a hydrophobic material, and it was difficult to form an antistatic layer with excellent surface properties using such a material. European Patent No. 328,981 discloses that an organic solvent-soluble thiophene derivative can be synthesized by electrolytic polymerization in an organic solvent system using a thiophene derivative and an organic solvent-soluble monomer dopant. However, though there is a tendency that this organic solvent-soluble polythiophene derivative is improved with respect to the affinity with a general-purpose curable monomer, it has become clear that when used for an antireflection film for a protective film of a polarizing plate, the monomer dopant elutes by an alkali treatment (saponification treatment), resulting in causing a problem that the conductivity is remarkably lowered.